Multiple-channel communication system



Nov. 12, 1929, A. H. TAYLOR A MULTIPLE CHANNEL COMMUNICATION SYSTEMFiled May 14, 1925 @ummm Patented Nov. 12, 19,29

'UNITED STA-TES:

Parana* OFFICE ALBERT H. TAYLOR, OF WASHINGTON, DISTRICT OF COLUMBIA,ASSIGNOR TO WIRED RADIO, INC., OF NEW YORK, N. Y.,

A CORPORATION OF DELAWARE MULTIPLE-CHANNEL COMMUNICATION SYSTEM.Application led May 14,

My invention relates broadly to high frequency signaling systems, andmore particularly to a multiple channel transmission system. l y Oneofthe objects of my invention is to pro- Vide a circuit arrangement forhigh frequency signal transmission whereby a plurality of independentsignaling circuits may be employed for independent modulation to impresssignaling currents up-ona common empliication system from which theindependent sets of signals may be conveyed to a carrier wave line Wiresystem oi' to an antenna ground radiating system.

Another object of my invention is to provide a circuit arrangement foreach of a plurality of independent high frequency signaling systems formaintaining said systems at a' constant operating frequency in suchmanner that the systems are prevented from interacting one upon anotherfor the multiple operation of several communication channels,

over the same line wire system or by radiation from the same antennaground system.

Still another ob]ect of my invention is to 4provide a signaling systemhaving a` plurality of channels for conducting communication withoutmutual interference over the. same carrier wave circuit or radiationcircuit in which quartz `crystals of Certain definite frequencies arearranged in circuit with the transmission channels for independentlycontrolling the frequency of each of the channels for preventing mutualreaction of one channel upon another in the process of simultaneousoperation of the circuits.

Still another object of my invention is to provide independent crystalcontrol circuits for a plurality oftransmitting circuits arranged todeliver signaling energy to the same carrier wave line wire system or tothe same antenna ground system in which the crystals are groundtodefinite frequenciesand connected in circuit withv independentoscillators for maintainingthe oscillators at the signaling frequencyfree of mutual inter-action.

A further object of my invention is toprovide crystal lcontrol circuitsfor a multiple channel communication 'system where independent 'electrontube oscillators may be 1925. serial no. 30,252.

maintained at difierent frequencies'separated from each other by only asmall percentage in frequency, while the power supply for the' electrontubes may, be derived from a common source and the oscillationsimpressed upon a common signaling circuit without inter-'action betweenthe oscillations.

lVhen -my invention is employed in radio transmission, I find that thesystem is par'- ticularly adapted to minimize fading effects bytransmitting. the same message on two simultaneous emitted frequencies.These lseparate frequencies seldom fade out simulquency is su'liicientto alter the time and the amount of fading, such a combination givesconsiderable protection against loss ofl a portion of the message byfading.' Vhen used for multiple channel communication forindependentmessages, traffic may be routed through both of thetransmitting circuits radiating independent messages simultaneously fromthe same antenna system. The antenna systems may be given particulardirection-al characteristics in such manner that, with Ithe transmittingstation located at the -Navy Department, Viashington, D. G., one

channel may be in direct communication with Europe, while anotherchannel is in simultaneous communication with the Philippines.

My invention makes use of the constant frequency characteristics of thepiezo electric effects vpcssessed by quartz crystals. I haveillustratedmy invention as applied to two-A channel communication systemwhere a pair of clectrontubes is arranged in a bilateral circuit foralternating current supply on the anodes or plates with the cathodes orfilaments lighted or heated from an alternating current power supply.Two independentI yquartz crystals are prepared by grinding the crystalsto two di'erent frequencies and the crystals connected around the inputcircuits of each of the oscillators for controlling the frequencythereof. The oscillators operate in alternation, one on one lobe of thealternating current power supply and the other on the opposite lobe ofthe alternating current power supply. The'outputs for the several tubesare Supplied to a common utilization circuit in a manner which will bemore fully described hereinafter/and simultaneous but independentcommunication maintained by modulation of the oscillator circuits.

My invention will be more clearly understood from the specificationhereinafter following by reference to the accompanying drawing whichdiagrammatically illustrates a two-channel communication systemembodying the principles of my invention. The circuit arrangementincludes electron tubes land 2 each haying a cathode 1a and-2-, a plateor anode 1b and 2b7 and a control electrode or grid lC and 2. The highpotential source for the electron tubes is derived from a common powersupply system. There are two quartz crystals provided marked @C1 andQC2, one controlling the frequency of the left-hand tube 1 and the otherthat of the right-hand tube 2. Separate sensitizing chokes 3 and 4 areeach connected in circuit y with the quartz crystals @G1 and Q02 andaround the input circuit of the tubes 1 and 2. The sensitizing choke 3has a free wavelength characteristic somewhat shorter than the frequencyto which the crystal QCl is ground. Similarly, the sensitizing choke 4thas a free wavelength characteristic somewhat shorter than the frequencyfor which the crystal Q02 is ground. Eachv choke isplaced in series withits own corresponding crystal. The anode or plate supply for the tubesis obtained from any suitable source through line system 5 and an anodesupply transformer 6 having primary winding I and secondary winding 8.It is well to use an alternating current supply of frequenciessuliiciently high to give a pleasing tone to the received signals. Ithas been found that frequencies between 210 and 600 cycles aresatisfactory for this purpose, although experiments have been made withfrequencies as low as 25 cycles. The anode 1b of tube 1 has radiofrequency choke 9 in series therewith and signaling key 10 is connectedin the plate circuit and with one end of the secondary S. The a-node,2bof the electron tubev oscillator 2 includes radio frequency choke coil11 in' circuit therewith and a signaling key 12 is series connected intocircuit with the opposite end of the secondary winding 6. At theinidpoint 14 in the secondary winding 8 a connection is taken to theshield 15 which entirely screens the oscillator and forms a groundconnection for the several circuits of the oscillator. rllhe output ofthe several Maasai necessary that the two quartz crystals do not differby more than a small percentage in frequency in order to have a singleadjustment of the condenser 17 suitable for Athe production ofoscillations of dilferent frej quencies; one in the right-hand tube 2and the other in the left-hand tube 1, but both pass through the commonplate coil system. Suppose, for example, the circuit is operated in theneighborhood of 4000 kes-thc crystals would then differ by as much as 10kc. from each other and only have a difference in fre quency ofonesfourth of one percent. This is too small from aipercentagepoint ofview to throw any of the circuits sensibly out of tune, and thereforethese two frequencies are both produced in the common platecoil systemwith a single setting of 1T, which can be so adjusted as to bring theoscillations of the two frequencies through with substantially thesameenergy or, if desired, the emphasis can be put on one or the otherof the two frequencies. It is understood of course that various forms ofcoupling may be used in this plate output circuit and that I do notintend the invention to be limited to the particular arrangement shown.

Any combination of plate circuit induetances may be used fordeliveringthe independent oscillations to the signaling systems. lllherecoupled circuits are used however the coupling should be quite close inorder that the rotation of the condenser 17 will adequately control thephase ofthe current in the plate circuit and therefore establish thecorrect phase relations for the development of the oscillations ofthecrystals. lt is advisable to use a certain amount of shielding asillustrated, but it is not absolutely necessary.

rllhc cathodes 1? and 2a are each heated from transformer 18 havingprimary winding 19 thereof supplied from the line wire system andsecondary winding 20 coupled thereto. Cathode 2n is connected across theends of the secondary winding 20 while a midpoint 21 is connected to theshield or ground 15 through conductor 22. The outputcircuits 16 and 1Tmay deliver signaling energy to the input circuit of a suitable poweramplifier 23 from which the energy may be impressed upon a carrier waveline wire system or the antenna radiating system represented at 24 and25. It is advisable to use a certain amount of negative C voltage inconnection with crystal control oscillators. IThese negative C voltagescan be obtained from the taps on the plate circuit transformer 6 withthe resistances marked 26 and 27 in series with these negative C tapsony the transformer winding 8 which prevent a rush of current in thetubes l and 2 when the plate voltage and grid voltages reverse. Duringthat half-cycle when a tube is nonoscillating, with this precaution itis perfectly possible to derive negative C voltage from' taps on theplate circuit transformer.

Resistance 27 is connected in series with radio frequency inductance 28and supplies the proper bias potential to the grid electrode lc of thetube l. The radio'frequency choke coil 29 is connected in series withresistance 26 and supplies the proper grid bias potential to the gridelectrode 2c. Each wave is modulated at the supply frequency. words, itconsists of the carrier wave with the usual side bands and can bereceived with either oscillating or non-oscillating detector in theusual manner. If crystal control were notused the point must beemphasized that it would not be possible to receive a smooth, clean-cutsignal unless the two crystals were ground identical and only one waveemitted, because the sequence of phase would be broken and the action ofthe lieterodyne or autodyne reception would be to give a very roughreceived tone like anA oscillating circuit receiving'a spark signal. Butthe damping of the crystals isso slight that feeble oscillations willhang over in the crystal from cycle to cycle, thus starting oifconsecutive oscillation groups as first one plate, then the otherbecomes positive in their proper sequences of phases. This is averyimportant point because it permits of a far superior type ofreception with oscillating detector. There is also a limit as regardsthe frequencies of the.

two waves emitted where it is not possible to key at telegraphic speedon account of the slowness of response of the crystal. Experiments havebeen made between 3000 and 4000 kes. however which show that at thesefrequencies satisfactory keying as high as twenty-five words per minuteisireadily possible and probably at considerably higher frequencies.These two frequencies are'not given off simultaneously, but inalternating groups, the

sequence'of phase in each group of frequen-l cies being maintainedintact due to the property of the respective crystals, thus permittingsmoothv reception with heterodyne or autodyne. No additionalcomplications are necessary in the power amplifier and antenna circuitsbecause these two emitted frequencies differ by so little in percentagetuning, that they will both readily pass through the power amplifiersystem and into the antenna.

I provide condensers 30, 3l, 32, 33, 34 and 35 at the points in theelectron tube circuits,

by passing radio frequency as indicated, for

the eificiency of the currents and improving system.

It will bevobserved that, ordinarily, when In other it isattempted tooperate a'plurality of oscillators anywhere in proximity of each otherthat the difticultyencountered is the tendency of the tubes to pull eachother into step, which by the inter-actionof the circuits entirelydestroys the multiple functioning of the system. By my arrangement ofquartz crystal control these several circuits are maintained absolutelyindependent in their operation even when separated at only a smallpercentage in frequency. i

While I have described my invention in certain particular embodiments, Idesire that it be understood that modifications may be made and that Iintend no limitations upon the invention other than are imposed by thescope of the appended claims.

Vhat I claim and desire toA secure by Iletters Patent of the UnitedStates is as follows l. A multiple channel communication systemcomprising in combination a plurality of high frequency generators, acommon energy supply system for alternately energizing said generators,a common energy utilization circuit connected with said generators,independent mechanically vibratile devices connected with each of saidgenerators for maintaining said generators at a constant operatingfrequency, whereby inter-action between said generators is prevented,and means for independently controlling each of said generators forproducing telegraphic signals in -said common energy utilizationcircuit.

,2. A multiple channel communication systein comprising in combination aplurality of high frequency energy generating circuits,'a common sourceof power supply for alternately energizing said circuits, a commonutilization circuit for the high frequency currents generated in -saidcircuit, independent piezo electric devices each ground to differentselected frequencies connected in each of said circuits for maintainingsaid circuits at sep arated operating constant frequencies. and meansfor controlling each of said circuits independently for impressingsignaling currents of different frequencies upon said ct nimonutilization circuit.

3. A multiple channel communication system comprising in combination apair of high frequency generators, a source of alternating currentpower' supply for alternately energizing each Aof said. generators, acommon energy utilization circuit connected with said generators, andpiezo electric devices each ground to a different operating frequencyconnected in shunt with each of said generators for maintaining saidgenerators at a constant operating yfrequency separated by a smallpercentage in frequency, N'WherebyL slightly separated signalingfrequencives may be impressed upon said common energy utilizationcircuit.

Il. A multiple channel communication sysof separated signalingfrequencies may be limpressed upon said energy utilization circuit.

5. A multiple channel communication system comprising inicombination apair of elecvtron tube oscillators, each of said tubes includiiw a ridfilament and late electrode b 2') 7 l p f input circuits connectedbetween the grid and filament of each of said tubes, and output circuitsconnected between the plate and filaments of each of said tubes, acommon power supply means for alternately energizing said circuits, acommon energy utilization circuit connected in said output circuits, andpiezo electric crystal elements each ground to different operatingfrequencies connected in the input circuits of each of said tubes formaintaining the frequency of the oscillations delivered to'said energyutilization circuit at slightly separated frequencies for producingindependent signaling currents in said energy utilization circuit.

G. A multiple channel communication system comprising in combination apair of electrontubes, each haring grid, filament and plate electrodes,an input circuit for each of said tubes including the grid and filamentelectrodes of said tubes, an output circuit for each of said tubesincluding the plate and filament electrodes of said tubes, a commonenergy supply system for said filaments, aii energy supply system foralternately energizing the plate electrodes of each of said elcctiontubes, a' common energy utilization circuit connected in said outputcircuit, and a constant frequency controlling circuit ccnnected in shuntwith the input circuits of each of said tubes whereby said tubesgenerate oscillations at separated fixed frequencies for delivery ofsignaling current to saidcnergy utilization circuit at separatedfrequencies.

7. A multiple channel communication systeni comprising in combination apair of electron tubes, each having grid, filament and plate electrodes,an input circuit for each of said tubes including the grid and-filamentelectrodes of said tubes, an output circuit for each of said tubesincluding the plate and filament electrodes of said tubes7 a commonenergy supply system for said filaments, an energy supply system foralternately energizing the plate electrodes of each of said electrontubes, a common energy utilization circuit connected in said outputcircuit, and constant frequency determining means comprising mechanicalvibratile elements connected in the input circuits of each of said tubesfor independently controlling the frequency of oscillations developed bysaid tubes, whereby signaling currents of separated frequenciesareimpressed upon said energy utilization circuit.

8. A multiple channel communication system comprising in combination apair of electron tubes, eachlliaving grid, filament and plateelectrodes, an input circuit for each of said tubes including;r the gridand filament electrodes of said tubes, an output circuit foi' each ofsaid tubes including the plate and filament electrodes of said tubes, acommon energy supply system for said filaments, an energy supply systemfor alternately energizing the plate electrodes of each of said electrontubes, a common energy utilization circuit connected in said outputcircuit, and a quartz crystal circuit connected in shunt with each of'said input circuits for independently controlling the. frequency of eachof said tubes, one of said quartz crystal circuits differing infrequency from the other of said quartz crystal circuits wherebysignaling currents of separated frequencies are impressed upon saidcommon energy utilization circuit.

9. A multiple channel communication system comprising in combination apair of electron tubes, each having Orid, filament and plate electrodes,an input circuit for each of said tubes including the grid and filamentelectrodes of' said tubes, an output circuit for each of said tubesincluding the plate and filament electrodes of said tubes, a commonenergy supply system for said filaments, an energy supply system foralternately energizing the plate electrodes of each of said tubes, acommon energy utilization circuit connected in said output circuit, anda device for sustainingv constant frequency oscillations connecte'd inthe input circuits of each of said. tubes foi independently controllingthe generation of a constant frequency by said tubes whereby signalcurrents separated from each other in frequency may be produced in saidenergy utilization circuit.

l0. A multiple channel communication system comprising in combination apair of electron tubes, each having grid, filament and plate electrodes,an input circuit for each of said tubes including the `grid and filamentelectrodes of said tubes, an output circuit for each of said tubesincluding the plate and filament electrodes of said tubes, energy supplymeans for said filaments, a separate energy supply` circuit foralternately energizing the plate electrodes of each of said tubes, a

' common energy utilization circuit connected in said output circuit, aquartz crystal circuit connected in shunt-'With each of said inputcircuits and an element connected in series "Wrh each of said crystalsand having a free weve-length less than the frequency of the crystalwith which it is connected for independently controlling 'the requencjy1of euch of said tubes, whereby signaling currents of separated:frequencies are impressed upon Suid common energy utilization circuit.

ALBERT H. TAYLOR,

